Loud-speaker



C. A. PERRY Nov. 13, 1956 LOUD-SPEAKER 2 Sheets-Sheet 1 Filed Oct. 23, 1951 INVENTOR. Chalk-(ea Ferry BY M@,M7 5

Nov. 13, 1956 c. A. PERRY 2,770,681

LOUD-SPEAKER Filed Oct. 23, 1951 2 Sheets-Sheet 2 zmQcec/ 16022 6 fieguenc INVENTOR. Char/65 4 Perry BYZMZL, Z1316 2 United States Patent LOUD-SPEAKER Charles A. Perry, Cleveland, Ohio, assignor to The Rola Company, Inc, Cleveland, Ohio, a corporation of Ohio Application October 23, 1951, Serial No. 252,651

2 Claims. (Cl. 179-115.5)

This invention relates to loud speakers generally and more particularly to the magnetic circuits for loud speakers and a method of operating such circuits.

The magnetic circuit of a loud speaker may be energized through a field coil from a uni-directional source of electrical current which produces a strong magnetic field in a core having an air gap within which is located a movable dynamic coil having a diaphragm physically coupled to the coil. Electrical oscillations varying at audio frequencies may be fed to the dynamic coil Which produces a varying field that interacts with the steady field of the field coil to produce a physical motion of the movable dynamic coil toward or away from the field coil according to the polarization of the core and the direction of the current flow in the dynamic coil. Thus the electrical oscillations are translated into physical motions which are coupled to a movable diaphragm to produce corresponding sound Waves.

Many speakers, although fed from a theoretically pure uni-directional current source, usually include varying or ripple components which may be induced into the dynamic coil to cause physical motions of the coil and diaphragm over and above the basic motion that the diaphragm is intended to execute. This is particularly evidenced in the case of speakers which have a source of low-voltage, direct current supply even though, as in the case of automobile speakers, the supply may be taken directly from batteries, since certain variations are reflected back from ancillary circuits.

A result of such overriding motions due to varying or ripple components in the unidirectional source of supply is the introduction of a hum into the audio reproduction of the speaker. In the past, steps have been taken to reduce the objectionable hum or to minimize it in connection with the operation of the speaker by introducing a copper slug in the magnetic circuit. The introduction of such a slug in the magnetic circuit is effective in reducing the undesirable introduction of varying components from the field coil into the dynamic coil at the higher audio frequencies. In like manner, the introduction of a series bucking coil in the magnetic circuit, even in lowvoltage battery type operations, is effective in reducing such introduction at the lower audio frequencies.

Accordingly, it is an object of this invention to provide an electromagnetic translating circuit and method of operation for a sound reproducer of the loud speaker type which may utilize a uni-directional source of energizing current which contains a varying component without the introduction of a disturbing effect in the dynamic coil.

Another object of this invention is the utilization of a shorted portion of the energizing field coil in place of a conventional copper slug to reduce undesirable interaction with the dynamic coil at the higher audio frequencies.

A further object of this invention is the provision of an electromagnetic translating circuit and method of operation which will reduce undesirable interaction 2,770,681 Patented Nov. 13, i956 "Ice between a field coil and dynamic coil throughout substantially the entire audio-frequency range of the sound reproducer. Other objects will be evident from the following description and the appended claims.

Briefly, in accordance with this invention there is provided an electromagnetic translating circu1t and method of operation for a sound reproducer wh1ch contemplates energization from a low voltage source of uni-directional current and which effectively reduces the introduction of any undesirable varying components from the supply into the dynamic operating coil which is movably supported within an air gap in the magnetic circuit. The electro-magnetic circuit includes in its preferred form a continuously wound field coil having a pair of taps spaced several turns apart intermediate its ends which are interconnected to short the turns therebetween. The portion of the field coil on one side of the shorted turns is adapted to be connected across the low-voltage source and the portion on the other side of the shorted turns is adapted to be connected in series bucking relation with the dynamic coil across a source of audio frequency electrical oscillations. The shorted coil turns effectively reduce the undesirable interaction between the coils at the higher audio frequencies by electrical absorption and dissipation of the varying component, while the series connected bucking coil effectively reduces such interaction at the lower audio frequencies by balancing out the varying component induced in the dynamic coil.

In the drawings, Fig. l is a diagrammatic illustration of a loud speaker construction showing the electromagnetic energizing system in cross section; Fig. 2 is a perspective View of the electromagnetic system showing the external coil connections and taps; Fig. 3 is a schematic diagram of the electrical portion of the magnetic circuits illustrating the electrical disposition and connections of the coils; Fig. 4 is a graphical representation of the interaction between the field and dynamic coils when a copper slug is introduced in the electromagnetic circuit; Fig. 5 is also a graphical representation of the inter-action between the field and dynamic coils when a series or bucking coil is introduced in the electronagnetic circuit; and Fig. 6 is a graphical representation of the interaction between the field and dynamic coils with a portion of the field coil shorted in electrical combination with a series bucking coil.

Referring now to Figs. 1 and 2 there is shown a preferred embodiment of a loud speaker construction having a diaphragm 1i} preferably in the: form of a cone to one end of which a voice coil form 11 is attached. The form 11 carries the usual voice coil 12 in concentric relation thereon. The electromagnetic transla portion of the speaker preferably embodies a shell-type core formed from a strip of metal that is bent to form an open frame having a front plate 21, a back plate 22, a top plate 23 and a bottom plate 24. The front plate has an opening 25 therein and the back plate has a pole piece 26 extending into the shell substantially parallel to the top and bottom plates thereof. The pole piece 26 terminates in a pole tip 27 which is concentrically disposed within the opening 25 and cooperates therewith to provide air gap 28 in which the voice coil 132 may be located to operate in the usual manner. The core may be attached to the cone assembly by suitable fastening members which extend through openings in a coupling portion 13 of the core housing. The fastening members may be in the form of bosses 29 which are extruded from the front plate El and are adapted to enter correspondingly shaped openings in the coupling portion 13. An energizing coil 3% is wound on the pole piece 26 and it is seen that four connections 31, 32, 33 and 34 are brought out from the 7 3 coil 39 and that the voice coil 12 also has end connections 15 and 16 extending therefrom.

As previously indicated, the uni-directional source of current supply for the energizing coil 30 may include pulsating or ripple components, particularly in the case of low voltage, direct current supplies. The undesirable pulsating or ripple components introduce a corresponding varying field in the electro-magnetic circuit which produces an overriding physical motion in the voice coil and diaphragm coupled thereto and thereby introduces an undesirable hum in the output of the speaker. Although copper slugs have been introduced in the magnetic circuit and have been satisfactory in reducing this hum by absorbing the ripple component, such reduction is only effective at the higher audio frequencies.

Referring now to Fig. 3, where like numerals designate like components, it is seen that the energizing coil 30 is in the preferred form of a continuously wound coil having a pair of taps 31 and 32 intermediate its ends spaced a few turns apart which are connected together to by-pass that portion 35 of the field coil. A source of uni-directional current supply is shown connected across a portion of the energizing coil 30 between one end connector 34 and the interconnected taps. It has been determined that the connection between taps 31 and 32 spaced three or four turns apart in the coil 30 will accomplish substantially the same result as a copper slug physically introduced in substantially the same position in the magnetic circuit of the loud speaker illustrated. It is a simple matter to wind a complete and continuous coil to the desired length and then bring out a tap and continue to wind a few additional turns and bring out the second tap. The Winding of the energizing coil is continued thereafter to provide another portion of the coil 40 which may be connected in the magnetic circuit in a manner to further assist the reduction of the interaction between the energizing field and dynamic coils at the lower audio frequencies as will be hereinafter more fully described.

As hereinbefore noted, a series coil connected in the proper direction, so that its induced hum voltage is opposite to that induced directly into the dynamic coil from the field coil is effective in neutralizing the hum or varying component under discussion at the lower audio frequencies. As is readily apparent in Fig. 3, the continuation 40 of the main energizing coil 30 beyond the shorted turns 35 is connected through the end connection 33 in series between the tap 31 on the shorted turns 35 and the connection 16 on the dynamic coil 12 in a direction to oppose the hum voltage induced in the dynamic coil. It has been determined that approximately sixteen to twenty additional turns beyond the shorted turns are sufiicient to balance out the varying component at the low frequency end of the audio response for the loudspeaker illustrated. A source of audio frequency electrical oscillations T is shown connected to the dynamic coil 12 between the top 31 and the end connection 15. Thus, the simple circuit illustrated in Fig. 3, is provided with an energizing coil 30 and a dynamic coil 12 having connected therebetween several shorted turns 35 on the coil 30, which correspond to a copper slug to reduce interaction between the energizing field and dynamic coils at the higher audio frequencies, and a series bucking coil 40 which reduces the interaction at the lower frequencies of the audio response to provide an overall substantially uniform reduction of the ripple component from a normal uni-directional source of supply in the dynamic operating coil. This arrangement and method of operation results in a uniform reduction of the undesirable interaction, eliminates unwanted hum in the audio output of the speaker, and results in a highly improved speaker performance.

It will be noted from Figs. 1 and 2 of the drawings that the continuous coil 30 is shown as layer wound on the pole piece 26 and that the shorted turns 35 and series connected portion 40 of the coil are axially disposed on the field coil 30. This arrangement is illustrative of the physical embodiment preferred but can be varied in accordance with the basic principles hereinbefore described without detracting from the operation and results. Thus, the coils may be axially disposed or layer wound in any physical configuration which will accomplish the electrical and magnetic results herein described.

Referring now to Figs. 4, 5 and 6, which are graphical representations of the developed reduction of the interaction hereunder discussion, the curves reflect induced voltage in terms of microvolts as an ordinate plotted against the audio response of the speaker on a logarithmic scale as the abscissa. Thus, in Fig. 4, there is graphically illustrated the reduction of the undesirable interaction between the field and dynamic coils when a copper slug is introduced in the magnetic circuit. The upper curve A represents the characteristic with the voice coil 12 a given predetermined distance within the air gap 28 and the lower curve C represents the characteristic with the voice coil 12 a given predetermined distance out of the air gap 28. The middle or intermediate curve B illustrates the characteristic performance with the voice coil 12 at a nominal or optimum position within the air gap 28 in relation to the construction of the particular speaker and the acoustic performance desired. It is readily apparent from the curves of Fig. 4 that the performance of the speaker improves at the higher audio frequencies by virtue of the progressive reduction of the interaction between the field and dynamic coils when the copper slug is introduced. Likewise, the performance when utilizing merely a copper slug, is relatively poor at the lower frequency end of the audio range.

Referring now to Fig. 5 which again is a graphical representation of the induced micro-volts in the dynamic coil versus the frequency range of the speaker when a series coil is connected in bucking relation between the energizing field coil and the dynamic operating coil, the three curves illustrated are representative of the performance characteristics when the number of turns in the series connected coil are varied. The curve designated D represents the greatest number of series connected turns and the curves E and F represent the performance as the turns are progressively reduced to the least number at F. It is readily apparent that the series connected bucking coil is quite effective in reducing the interaction between the field and dynamic coils at the lower audio frequencies and progressively becomes less effective as the frequency increases in the audio range.

Referring now to Fig. 6 which also graphically represents micro-volts of induced voltage in the dynamic coil 12 plotted versus the frequency range of the speaker, there is illustrated the performance characteristic of the speaker with respect to the induced voltage of the dynamic coil when the magnetic circuit of Fig. 3 is utilized as the electro-magnetic translating medium in a speaker of the type under consideration. It is readily apparent from this representation that the curve G illustrated in Fig. 6 represents an optimum desired performance characteristic in that it is substantially uniform throughout the audio range of the speaker. The shorted turns 35 in the magnetic circuit of Fig. 3 operate in the circuit to reduce the interaction at the higher audio frequencies and the series connected turns 40 operate to reduce the interaction at the lower audio frequencies, thus improving the overall performance of the loud speaker.

Thus, the combination of the shorted portion 35 of the energizing field coil 30 with a further portion 40 of that coil connected in series bucking relation to a dynamic coil 12 in a loud speaker magnetic circuit produces a highly improved performance of the loud speaker by virtue of the uniform reduction of undesirable interaction between the field coil and dynamic coil in the magnetic circuit. Likewise, the utilization of several shorted turns in place of the conventional copper slug enables the conservation of the critical material such as copper and also provides a considerable degree of flexibility in the manufacture of loud speakers as well as in accomplishing varying performance characteristics corresponding to different loud speaker constructions and acoustic responses.

I have shown and described What I consider to be the preferred embodiment of my invention along with suggested changes and modifications, but it will be obvious to those skilled in the art that other changes and modifications, particularly with respect to variations in the construction and connections of the energizing field coil and its efiectiveness, may be made without departing from the scope of my invention as defined by the appended claims.

I claim:

1. In a loudspeaker having a continuously wound energizing field coil and a cooperating dynamic voice coil in a common magnetic operating circuit, wherein a portion of said field coil is energized from a uni-directional current source having a varying component and said dynamic coil is energized from a source of audiofrequency varying electrical oscillations, the method of neutralizing the varying component in the common magnetic field throughout the audio frequency range of the speaker consisting of, balancing out the varying components induced in the dynamic coil at the lower audio frequencies by connecting a portion of said field coil in series bucking relation with said dynamic coil across the audio source, and electrically absorbing and dissipating the varying component at the higher audio frequencies by electrically by-passing a plurality of field coil turns from the energized portion of said field coil to said series connected bucking portion of said field coil.

2. A loudspeaker comprising in combination, a shelltype coil having a pole piece centrally disposed therein,

said pole piece forming an air gap at one end with said core, a dynamic voice coil operatively located for movement within the air gap, a diaphragm coupled to said voice coil, an energizing coil continuously wound in layer form throughout the length of said pole piece, a pair of taps spaced inward a plurality of turns from each end of the coil and from each other and extending from said layer wound energizing coil, end taps extending from each end of said energizing coil, means connecting the end of said energizing coil adjacent said dynamic coil in series bucking relation to one end of said dynamic coil, to oppose the varying field component induced in the dynamic coil from the energizing coil at the lower audio frequencies, an electrical connection between the two intermediate taps on said energizing coil adapted to short the portion of the coil therebetween to electrically absorb varying components of energizing coil magnetic field at the higher audio frequencies, means for connecting a source of audio frequency electrical oscillations between said interconnected taps and the other end of the dynamic coil, and other means for connecting a source of unidirectional current having a varying component between said interconnected taps and the other end of said energizing coil.

References Cited in the file of this patent UNITED STATES PATENTS 1,795,214 Kellogg Mar. 3, 1931 1,830,402 Miessner Nov. 3, 1931 2,274,296 Hughes et al. Feb. 24, 1942 2,286,123 Steers June 9, 1942 FOREIGN PATENTS 546,812 Germany Mar. 17, 1932 

